Ever since I was a wee little lad, I have heard the common “Big Rock” challenge to God’s existence: “If God is omnipotent, can He make a rock so big that he can’t lift it?”
When it’s asked for fun as a discussion of logic conundrums, it’s one thing. But when it is actually believed to be a successful argument against God’s existence, it’s just pathetic. And, sadly, some do think it is an argument against God’s existence.
Then, in today’s Best of the Web Today feature in the Wall Street Journal, I read a very concise discussion & refutation of it by James Taranto — and he was discussing politics and constitutional logic, not theology, so it was pleasing all the more being a surprise appearance. I’ve explained the illusion behind the question to others before, but he does it so concisely that I thought it worth mentioning here:
Think about that old Philosophy 101 question: If God is omnipotent, can he make a rock so big that he can’t lift it? It seems like a puzzle, but the answer is clearly no. The premise that God is omnipotent leads to the conclusion that he can both make and lift a rock of any size. “A rock so big that he can’t lift it” is a logically incoherent construct, not a limitation on God’s power.
The person asking the question simultaneously affirms and contradicts the premise of God’s omnipotence, creating a non-question. It’s like asking, “Can God be simultaneously omnipotent and not omnipotent?” The answer is no, as is the answer to its more fuzzily-worded “rock” puzzle variation. So when posed that question we are free to answer “No,” understanding what the questioner probably does not: that the answer has nothing to do with a limitation on God’s abilities and everything to do with limitations on what kinds of rocks can exist. (Like telling someone: “Using one color only, paint this birdhouse completely red and not-red.” Your inability to do so relates to what colors can logically exist, not your ability to paint birdhouses.)
Taranto’s explanation is short and sweet, methinks. So, if you’ve ever been stumped by the question, don’t be. Just answer “No” and recommend that the individual take a good freshman logic course at his or her local community college.